1. Field of the Invention
The present invention relates to shutoff-opening devices, for example, for use in a fluid control apparatus included in semiconductor manufacturing equipment, and more particularly to shutoff-opening devices comprising a plurality of valves, to be provided at the fluid inlet and/or fluid outlet of a fluid controller such as a massflow controller and adapted to close or open a plurality of fluid channels.
2. Description of the Related Art
FIG. 4 shows a conventional shutoff-opening device 81 installed at the fluid inlet side of a massflow controller (see JP-A-172265/1993). The device 81 comprises a first on-off valve 82 remote from the inlet (at left in the drawing), and a second on-off valve 83 close to the inlet (at right in the drawing). The first on-off valve 82 comprises a first valve main body 84 and a first valve actuator 86. The second on-off valve 83 comprises a second valve main body 85 integral with the first valve main body 84, and a second valve actuator 87. The first valve main body 84 has a first fluid inflow channel 88, and a first fluid outflow channel 90 communicating with the inflow channel 88 via a valve chamber 89. The communication between the channels 90 and 88 is shut off or established by operating the first valve actuator 86. The second valve main body 85 has a main outflow channel 91 always communicating with the outflow channel 90 of the first valve main body 84 for discharging a first fluid toward the inlet of the massflow controller, a second fluid inflow channel 93 having one end opening at the bottom side of the second valve main body 85 and the other end communicating with a valve chamber 92, and a second fluid secondary outflow channel 94 having one end communicating with the second fluid inflow channel 93 via the valve chamber 92 and the other end always communicating with the main outflow channel 91. The communication between the channels 94 and 93 is shut off or established by operating the second valve actuator 87. Indicated at 95, 96 in FIG. 4 are diaphragms which are movable upward or downward within the respective valve chambers 89, 92 with the upward or downward movement of respective valve stems 97, 98 by the operation of the valve actuators 856, 87, whereby the respective inflow channels 88, 93 are shut off or opened.
With shutoff-opening devices of the type described, it is usual practice to pass a first fluid (e.g., process gas) through the device, thereafter pass a second fluid (e.g., purge gas) with the flow of first fluid interrupted, thereby discharging the first fluid from the device and replacing the first fluid by the second fluid, and Subsequently pass the first fluid again. The first fluid and the second fluid are alternatively passed through the conventional shutoff-opening device 81 in the following manner.
First, the first valve actuator 86 and the second valve actuator 87 are operated to open the first on-off valve 82 and close the second on-off valve 83, whereby the first fluid is caused to flow into the inlet of the massflow controller via the inflow channel 88 and the outflow channel 90 of the first valve body 84 and through the main outflow channel 91 of the second valve main body 85. At this time, the second fluid secondary outflow channel 94 is filled with the first fluid. The actuators 86, 87 are then operated to close the first on-off valve 82 and open the second on-off valve 83, whereby the second fluid is introduced into the inlet of the massflow controller via the second fluid inflow channel 93, the second fluid secondary outflow channel 94 and the main outflow channel 91. At this time, the second fluid flows while driving out by the pressure thereof the first fluid remaining in the secondary outflow channel 94 and the subsequent main outflow channel 91, and the first fluid outflow channel 90 of the first valve main body 84 is to be filled with the second fluid.
In the case where the first fluid and the second fluid are alternatively passed through the shutoff-opening device upon a change-over, it is very important to replace one fluid by the other fluid quickly to assure the fluid to be passed of its purity.
The conventional shutoff-opening device 81 has the following problem. When the second fluid is introduced into the second on-off valve 83 of the conventional device 81 through the second fluid inflow channel 93 after the passage of the first fluid, the first fluid remaining in the first fluid outflow channel 90 of the first valve main body 84 becomes mixed in small portions with the second fluid, presenting difficulty in replacing the first fluid by the second.